Field of the Invention
The present invention relates to apparatus for scanning an original in a copying machine and more particularly to such type of scanning apparatus in which an original to be copied is scanned by first and second reflecting means driven to move in the same direction at the velocity ratio of 1:1/2 employing the principle of a running block.
The above mentioned type of apparatus, that is, the scanning apparatus adopted to scan originals to be copied in which the first and second reflecting means are moved in the same direction at the velocity ratio of 1:1/2 employing the principle of running block in order to keep the optical length between the original and the lens always constant, are well known, for example, from U.S. Pat. Nos. 3,330,181; 3,431,053; 3,614,222; 3,884,574; 3,914,044 and 3,832,057 and Japanese Patent Application laid open Nos. 75228/1973 and 60235/1975, Japanese Utility Model Application Publication No. 45332/1976 and Japanese Utility Model Application Publication No. 3297/1972.
These known apparatus have in common a construction wherein the movable carriage for the second reflecting means is provided with a block rotatably mounted thereon and with a wire laid round the block with one end of the wire being fastened to a stationary part of the associated copying apparatus. A portion of the wire is fixedly connected with the movable carriage for the first reflecting means. According to the arrangement, movement of the first reflecting means in a predetermined direction causes the wire to draw the block and thereby the second reflecting means is moved in the same direction as the first reflecting means and at a velocity of 1/2 that of the first one.
In the known apparatus disclosed in the above mentioned first five U.S. Patents specifications, there is used a spring to move the first and second reflecting means back to their respective home positions from their end positions of forward movement. One end of the spring is secured to the carriage of the second reflecting means and the other end to a stationary part of the copying apparatus. Thus, as the first and second reflecting means are moved forward to scan the original, a spring tension is stored in the spring. In other words, the forward movement of the reflecting means is carried out against the spring force. However, such arrangement of the apparatus has a particular disadvantage. Since the spring force is gradually increased with the forward movement of the first and second reflecting means, the mode of movement of the two reflecting means is apt to become unstable. This in turn causes an unstable scanning of the original. Another drawback is that in order to drive the first and second reflecting means to move against the spring force, there is required a motor of high power. This requirement will be enhanced when a spring of high elastic modulus is used so as to move back the first and second reflecting means more rapidly. Furthermore, the use of such a spring produces a greater impact when the first and second reflecting means are stopped at their home positions. This impact may cause a disorder of the scanning optical system and trouble with the associated copying machine.
Contrary to the above described known apparatus, the above mentioned U.S. Pat. No. 3,832,057 discloses a scanning apparatus in which a spring as described above is not used. But, this known apparatus is extremely complicated in structure. In order to move the first and second reflecting means forward at the velocity ratio of 1:1/2, this known apparatus employs a driving pulley for the first reflecting means and another driving pulley for the second one the diameter of which is 1/2 that of the first driving pulley. These two driving pulleys are coaxially mounted and have two separate wires, one for the first pulley and the other for the second pulley. The one wire wound around the first driving pulley is fastened to the carriage for the first reflecting means and the other wound around the second driving pulley is fastened to the carriage for the second reflecting means. In this manner, when the two pulleys are rotated by a motor, the first and second reflecting means are moved forwardly in the same direction and at the velocity ratio of 1:1/2. When the first driving pulley is reversed in its driving motion so as to pull the first reflecting means in the return direction, a third wire is brought into operation to pull a block provided rotatably on the carriage for the second reflecting means. The one end of the third wire is fastened to the carriage for the first reflecting means and the other end is fastened to a stationary part of the copying apparatus after passing around the above block. As will be understood from the above, in this known scanning apparatus, the principle of the running block is used in moving the first and second reflecting means back to their starting positions and therefore the structure is very complicated.
All of the apparatus disclosed in the above mentioned Japanese publications use no spring for returning the reflecting means back and use only one driving pulley so that the forward and backward movement of the first and second reflecting means may be effected using substantially only one pulley wire. The principle of this prior art arrangement is shown schematically in FIG. 3a for the purpose of reference.
Referring now to FIG. 3a, a driving pulley driven by a reversible motor is designated by 31 and a wire 35 is wound around the pulley with several windings. 32, 33 designate stationary blocks positioned in predetermined fixed positions within the copying apparatus. 34 is a running block rotatably mounted on a carriage for the second reflecting means. The one end of the wire 35 is fastened to a fixed position 36 and the other end to another fixed position 37 respectively within the copying apparatus. The wire extends from the position 37 to 36 passing around the running block 34, the stationary block 32, the driving pulley 31, the stationary blocks 33 and again the running block 34 successively in this order. The carriage for the first reflecting means is connected with the wire at its segment 40 extending between the blocks 32 and 34. A rotation of the driving pulley in the direction of arrow 39 will drive the carriage of the first reflecting means connected with the wire 35 as well as the carriage of the second reflecting means having the running block 34 mounted thereon in the direction of arrow 39' at the velocity ratio of 1:1/2 to scan an original. At this time point, the segment of the wire 35 extending on the side of the stationary block 33 pulls the running block 34 for the forward movement. After the completion of a scanning of the original, the first and second reflecting means can be moved in the opposite direction to the arrow 39' at the velocity ratio of 1:1/2 by reversing the rotation of the driving pulley. During this phase of operation, the wire 35 pulls the running block 34 by its segment extending on the side of the stationary block 32. The range in which the connection point of the carriage of the first reflecting means with the wire 35 is allowed to move, is indicated by lo.
While the known original scanning apparatus illustrated in FIG. 3a does not have those disadvantages as the previously described known apparatus have, it has other drawbacks. One drawback is that the apparatus becomes relatively long in size in the direction of movement of the running block 34. This is because the running block 34 must be moved between the stationary blocks 32 and 33 together with the connecting point 40 of the carriage of the first reflecting means with the wire 35. Moreover, the stationary block 33 has to be positioned at least beyond the end of the path of movement of the running block 34. This constitutes a limitation to the arrangement of apparatus. A further drawback involved in this known apparatus is that since the wire 35 must be a long one, it easily becomes slack over a period of time.